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Source: Journal - automotive use technology
Abstract: This paper describes the product characteristics and technical conditions of a kind of non drying silane modified polymer sealant, and summarizes its construction conditions, injection equipment and comparison with high-temperature sealant with an application example of an automobile production line.
Key words: no drying; characteristics; construction conditions; glue injection machine
Preface
Body weld sealant is one of the common materials used for body weld sealing in automobile coating line. It is mainly used to fill and seal the structural gap of body plate, and its main functions are sealing, waterproof and shock absorption. At present, polyurethane sealant is the most widely used body sealing material in most automobile coating lines, with two major characteristics: one is slow curing speed, which requires high temperature baking to set and cure; the other is carbon dioxide generated during curing, which causes air holes in the adhesive layer and produces a certain amount of VOCs, which will have a certain impact on people and the environment. With the development and progress of automobile industry, the application of aluminum body has developed rapidly, and a new type of dry free sealant material has been recognized in the application of aluminum body.
Based on an automobile production line, this paper analyzes the application of the dry free sealant.
1. Introduction of dry free sealant
1.1 introduction to rubber products
Sikaflex-221 sealant developed by Sika company is a one component silane modified polyurethane adhesive sealant, which is composed of polymer, filler, dehumidifier, plasticizer, catalyst, etc. The biggest feature of the adhesive is that it reacts with the moisture in the air and solidifies to form a permanent elastomer, which eliminates the need for high temperature baking of the conventional weld sealant on the automobile production line. It has many advantages, such as many uses, anti sag, single component, low odor, no drying, aging and weathering.
1.2 technical conditions
See Table 1 for details of technical conditions
Table 1 Comparison of technical parameters between dry free sealant and high temperature sealant
Compared with conventional PVC high temperature polyurethane sealant for automobile, it has obvious differences in material, curing mechanism, hardness, extrusion force and elongation at break, and other technical parameters are basically the same. Therefore, it can be judged that there is no risk in product performance, quality and other aspects when the non drying silane modified polymer sealant is used for automobile weld sealing, which can be applied to filling and sealing the structural gap of automobile body plate.
1.3 characteristics of rubber products
(1) Adopting the natural curing mechanism of moisture, no need of conventional baking, saving the investment cost and kinetic energy cost of the factory;
(2) The adhesive is neutral and free of solvent, isocyanate and PVC particles. It is odorless during curing, low VOC release, environmentally friendly and suitable for personal contact;
(3) Good adhesion can be obtained to substrate without primer;
(4) - 40 ℃ ~ 90 ℃ keep long-term elasticity, not easy to bubble, not crack, good deformation and extrusion, easy to construction.
2. Application of dry free sealant
The coating line of an automobile factory is an aluminum body sealing line, which mainly produces aluminum logistics electric vehicles and small passenger vehicles. Its process is aluminum body in white coating → high temperature weld sealing → glue drying → aluminum body outer plate (or plastic outer plate) skin → aluminum body outer plate (or plastic outer plate) edge sealing. The conventional high-temperature aluminum sealant shall be used for the sealing of high-temperature welds, which shall be cured after baking at 140-160 ℃; the non drying polymer sealant shall be used for the edge sealing of the body outer panel, which shall be naturally cured by moisture. Because the dry free polymer sealant does not need to be baked in the oven, it is commonly known as normal temperature sealant.
2.1 construction conditions
Requirements for materials: applicable base materials include galvanized sheet, cold rolled sheet, aluminum, plastic and other automotive materials. At the same time, the surface of the substrate shall be clean and dry without grease, oil and dust.
Chemical resistance: the sealant has good resistance to fresh water, sea water, lime water, sewage, dilute acid and alkali solution, short-term resistance to fuel oil, mineral oil, vegetable oil, animal fat and crude oil, and is not resistant to organic acid, alcohol, concentrated inorganic acid-base solution or solvent.
Construction methods: (1) unpack the rubber products, and then replace the rubber products according to the requirements, so as to avoid blistering between the base material and the rubber products; (2) start the rubber pump, send the rubber products to the gun station, and then glue the parts needed by the body.
Surface painting: this kind of adhesive can be painted after the surface is dry, and the matching test shall be done before painting.
2.2 application effect
Before application, a series of experiments were carried out in the laboratory under 10 times limit conditions. After 3 months, the non drying silane modified polymer sealant has obvious advantages in weather resistance and durability compared with the high temperature polyurethane sealant. As shown in Figure 1, under 100 times magnifying glass, the surface of the polyurethane adhesive began to crack and distribute more, on the contrary There was no cracking in the dry free silane modified polymer adhesive.
Figure 1 Comparison between silane modified polymer and polyurethane
When coating on the real vehicle on site, due to the viscosity of the rubber products is larger than that of the conventional coating high-temperature weld sealant, the glue delivery rate is relatively slow, and the resistance of rubber scraping is relatively large, but the operation is basically not affected, on the contrary, the sealing property of the coating is relatively tight and flat, as shown in Figure 2.
Fig. 2 legend of rubber coating under wet film condition
Figure 3 status of rubber products after drying
After the surface of the rubber coated on the body surface is dry, when touching and pressing by hand, the surface is smooth and elastic, as shown in Figure 3; when tearing, it has strong tensile strength and ductility; after 30 minutes of intensive rain test, the body has good sealing performance and no water leakage at the weld joint, achieving the sealing effect.
3. Selection of glue injection machine
In the practical application of non drying silane modified polymer sealant in the line, the single car usage is about 1kg, so combined with the production rhythm and the characteristics of the rubber products, the 5-gallon raw material barrel packing glue injection machine and the matching system accessories are selected, see the glue injection machine connection system figure 4 for details. There are certain requirements when selecting the glue injection machine, such as the relevant parameters of the main pump, pipeline, heating function and gun station, etc.
Main pump of glue injection machine: the glue injection machine packed in 5-gallon raw material barrel shall be selected. The pressure ratio of the equipment shall be 65:1, one reciprocating displacement shall be 0.18l, the rated air inlet pressure shall be 0.5MPa, the use viscosity shall be less than 5 * 105 centipoise, and the size of the pressure plate shall be φ 285mm. In addition, the working air pressure shall reach 0.6MPa, the maximum output pressure shall reach 28Mpa, and the flow rate of 60 cycles / minute shall be 6L / min.
Fig. 4 connection system of glue injection machine
Glue supply pipeline: the pipeline adopts high-pressure seamless steel pipe, which is connected by flange (direct welding between pipeline and pipeline is prohibited). The single-sided aluminum foil rubber plastic insulation layer is set outside, with a thickness of 20mm.
Heating device: according to the temperature requirements of the rubber products, the external surface of the rubber pipe is equipped with a tracing heating device for the whole process of heating and heat preservation, and the pressure plate heating function is increased, so as to keep the viscosity of the rubber products within the process requirements in winter.
Rubber conveying gun station: each gun station is equipped with a high-pressure filter (5000PSI pressure), a pressure regulator (more than 3500psi pressure), a pressure gauge (5000PSI maximum range) and a high-pressure ball valve. The outlet of the gun station shall ensure the accuracy of the filter screen and shall not block the gun. Outlet pressure: 100-250bar, adjustable; outlet flow: ≥ 600cc / min.
4. Precautions
In the practical application process of non drying silane modified polymer sealant, due to its characteristics and technical requirements, some matters need to be noted, as follows:
(1) The lower the temperature, the lower the moisture content in the atmosphere, and the slower the reaction process. Therefore, it is required to construct under the temperature lower than 5 ℃ or higher than 40 ℃.
(2) Once the plastic packaging is opened, it must be used up in a relatively short time. Because the rubber is cured by moisture, if the rubber is in contact with air for a long time, the rubber is easy to surface dry, which is easy to cause blockage of the rubber gun and the rubber pump. Therefore, after the glue gun is used, if it is not used for more than 20 minutes, it is necessary to immerse the gun head in sealing liquid or vaseline to prevent the gun head from contacting with air; after the full barrel of glue is opened, it is required to inject the glue pump and pipeline at the first time, and the surface contacts with air; in addition, it is also necessary to timely handle the residual glue on the surface of the equipment body.
(3) When finishing or finishing, it must be carried out before the surface of the rubber products is dry. If the surface of the rubber products is dry, it must be coated on the surface in advance with the finishing agent or lubricant matched with the rubber products.
(4) If the rubber products need to be removed, the soaked surface can be properly coated with solvent before curing, and then removed with scraper; once cured, it can only be removed by mechanical methods.
(5) After painting, the rubber must be cured completely before baking at high temperature, otherwise the hardness and elasticity of the rubber will be reduced, and the paint surface will crack.
(6) After gluing the hand and exposed skin, wash them with industrial hand sanitizer and water immediately, and do not use solvent.
5. Conclusion
In the environment of environmental protection, energy saving and low-cost automobile manufacturing, it is a new technological innovation to replace high-temperature seam sealant with silane modified polymer sealant at room temperature. Through practical application, the application of the silane modified polymer sealant saves the investment of drying equipment, energy consumption, no VOC emission, and really achieves the effect of zero pollution.
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